Process for the formation of olefines



I aflin hydrocarbons.

Patented Jan. 23, 1934 rnocnss'ron THE FORMATION OF OLEFINES} Per K. Frolich,- Cambridge,

C. Boeckeler, St. Louis,

Mass., and Benjamin Mo.; said Frolich assignor to Standard. Oil Development Company, a corporation of Delaware No Drawing. Application May 2, 1929 SeriaLNo. 360,000

in a process for the production of 4 Claims.

to improvements more specifically comprises an improved process for the production of olefines from saturated parunderstood from the It is well known bons decompose under the The process will be fully following description.

that the paraffin hydrocariction of heat, and

that olefines are formed therefrom. The process 0 is not a simple one, however, but is the result of several reactions. two ways in which The followin and g equations show decomposition occurs: (1) CnH2n+3 CnH2n+H2 to proceed without the second and in this way a large share of olefines corresponding to. the paramn used is formed. In other dehydrogenation words, a simple is obtained without any substantial production of saturated hydrocarbons such as methane.

In the operation of drocarbon, heavier than methan the process a parafiin hye, such as ethane,

propane, butane, pentane and the like, or a mixture of such parailins, is vaporized at low pressure and is passed through a which the temperature is a suitable catalyst is placed.

reaction zone in regulated and in which The temperature of the reaction zone depends somewhat on the eral is below 700 The temperature to particular catalyst, but in gen- C. and above about 450 C. some extent depends also on the particular hydrocarbon being treated and is generally higher for lower molecular weight hydrocarbons.

The time of reaction also varies with temperature and the particular catalyst. If

the time is too short the yield of olefine is small,

and if toolong carbon formation and polymerization reduce. the yield. The space velocity used. in terms of volume of hydrocarbons per minute per volume of reaction space, is advantageously in the neighborhood of 13, although it has been as low as terms given.

Metallic catalysts have been 1.8 and as h igh as 108 in the found satisfactory, and mixtures of metallic oxides after reduction with methanol, hydrogen, por or otherwise are preferred hydrocarbon vaalthough other types of dehydrogenation catalysts may beused. Catalysts containing zinc oxide and another oxide of a metal which has-two or more valences have been found to be satisfactory, such as 30 molecular per cent of zinc oxide and '70 molecular 30 per cent of chromium oxide, or other proportions of the same elements, or zinc oxide and molybdenumoxide.

It is also advantageous to dilute the hydrocarbon with other gases such as nitrogen or Water vapor or hydrogen which tends to prevent carbon deposition.

As an example of the process, the catalyst is prepared in the following manner-25 cc. ofa suspension of Zn(OH)z containing 0.107 gr. per cc. is added to 38 cc. of a solution of CI'O3 containing 0.1645 gr. per cc. All but a trace of the Zn(OH)-2 dissolves. 12 cc. of pumice stone previously digested in concentrated HCl is then added and the solution evaporated and the solid dried at 100 C. Analysis shows the metals to be in the mol. proportion of 30.2% zincand 69.8%

v chromium.

The catalyst is then reduced with pure methanol, gradually increasing the temperature from 80 C. to 250 C. in 45 minutes. The catalyst is then placed in a quartz tube 18" by in diamstar and wound with resistance wire for electrical heating.

Propane is then passed through the tube at 35 a rate of 9.6 liters per hour, being preheated before entering the reaction tube. In terms of space velocity, the rate of flow is 13.4 volumes of propane vapor per minute per volume of reaction space and the temperature is maintained at about 635 C.

The ofitake gas is collected and gives the fol lowing analysis:

Propylene 14.3% Ethylene .2 Hydrogen 26.1 Residue 59.4

The residue is substantially entirely propane. There is some carbon deposition.

In a second experiment similar to the above. using a catalyst of the same composition as in the previous example and the same rate of flow, but with a temperature of 505-530 C. and with nitrogen as a diluent, about 11.7 mol. of the propane was converted to propylene without the formation of ethylene and with no visible carbon deposition.

The process may be applied as above noted to pure hydrocarbons heavier than methane or to parafiln hydrocarbons mixtures of hydrocarbons, although in the latter case it is preferable to use closely fractionated cuts. The unchanged hydrocarbon may be recirculated to increase the yield of olefines as will be understood-first separating the olefines, for example by absorption in sulfuric acid or otherwise.

The invention is not to be limited by any theory of the mechanism of the reaction nor by any example given merely by way of illustration, but only by the following claims in which it is desired to claim all novelty inherent in the invention.

We claim:

1. An improved process for the treatment of heavier than methane for the production of olefines of the same number of carbon atoms without formation oi substantial quantities or lower molecular weight olerlnes, which comprises passing the hydrocarbons through a reaction zone at a temperature between the approximate limits of 450W and 700 C. in contact with a catalyst, composed of a mixture of zinc oxide and chromium oxide, which has been subjected to reducing conditions before coming in contact with the paramn hydrocarbons.

which comprises 2. Process according to claim I in which the rate of flow is be ween the limits of 1.8 and 108 volumes of hydrocarbon per minute per volume of reaction space.

3. An improved process for the treatment of parafiin hydrocarbons heavier than methane for the production of olefines of the same number of carbon atoms without formation of substantial quantities of lower molecular weight olefines, passing the hydrocarbons through a reaction zone at a temperature between the approximate limits of 450 and 700 C. in contact with a catalyst composed of about 30 mol. per cent of zinc oxide and '70 mol. per cent of chromium oxide.

a. An improved process for the formation of olefines from parafiln hydrocarbons heavier than methane which comprises passing the hydrocarbons over a catalyst comprising about 30 mol.

per cent zinc oxide and '10 mol. per cent chromium oxide.

PER K. FBOLICH. BENJAMIN C. BOECKELER. 

